Propeller



Aug. 9, 1932. M. A. SMITH, JR

PROPELLER Filed March 12, 1932 INVENTOR. M /7. Smz'i'h Jr: 72% ATTORNEYS Patented Aug. 9, 1932 UNITED STATES PATENT OFFICE MARSHALL A. SMITH, TIL, OF SOUTH BEND, INDIANA, ASSIGNOR TO BENDIX AVIATION V CORPORATION, OF SOUTH BEND, INDIANA, A CORPORATION O]? DELAWARE PROI'ELLER Application filed March 12, 1932. Serial No. 598,509.

This invention relates to propellers and more particularly to the construction of propeller blades. r

In the operation of rotating propeller blades, it is well known that the velocity of the air stream traversing the aerofoil sections of the blades varies as the distance along the length of each blade. When a five foot propeller blade, for example, is revolving at 10 2000 revolutions per minute, the air -velocities across those aerofoil sections adjacent the tip of the blade are approximately between 900 and 1000 feet per second, while the air velocities across the remaining aerofoil sections of the blade, decrease as the blade root is approached.

It has been found that for air velocities below approximately 900 feet per second, aerofoil blade sections having a relatively flat thrust face and a convex back or suction face are very efficient. However, in instances when air velocities exceed approximately 900 feet per second, it has been determined that the usual aerofoil blade sections do not yield a substantially high propeller efficiency.

By the present invention, it is proposed to construct an efficient propeller blade for normal operation at approximately 2000 revolutions er minute, although modifications for difl rent rotative speeds of the propeller blade are claimed within the spirit of this invention. The proposed construction consists in convexing that portion of the surface of the thrust face where the velocity of the air stream reacting with it, in normal operation, will exceed approximately 900 feet per second, although it is to be understood that the invention is not limited to the velocities mentioned.

One of the objects of the present invention is accordingly to provide a novel pro eller construction whereby the efficiency 0 propellers operating at relatively high speeds is materially increased. I

' Another object of the invention is to provide a propeller blade with novel blade surfaces so arranged that the reaction of the air stream on the blades of the rotating propeller is appreciably increased.

-tailed description when taken in connection with the accompanying drawing. It is expressly understood,'however, that the drawmg is for the pur oses of illustration only and is not to be ta en as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawing wherein like reference numerals refer to similar parts throughout the several views:

Fig. 1 is a side view of a propeller blade;

Figs. 2, 3, 4, 5, 6, 7, and 8 are cross sectional views of the blade in Fig. 1 taken at spaced intervals longitudinally of the blade.

Referring to the drawing, there is disclosed therein a propeller blade 1 having leading and trailing edges 2 and 3, respectively, the said blade being adapted to be inserted in the usual propeller hub 4 shownin dotted lines. As shown, Figs. 28 inclusive illustrate the various cross sectional shapes imparted to the blade 1 at articular intervals along the longitudinal axis thereof, Fig. 2 illustrating the shape of the blade at a position 13 92; of the length of the blade, Fig. 3 the shape at 25% of the length, etc. In these figures, it will be observed that the blade is constituted by a thrust face 5 and a camber face 6 and as illustrated, the blade is of conventional form from its root end to a point approximately 62 of its length, that is, the thrust face is gradually flattened as the central portion of the blade is approached. However, from approximately 62 of the length, to the tip of the blade a novel aerofoil section, comprising a relatively cambered thrust face, is imparted to the blade. Figs. 7 and 8 illustrate the cross sectional views corresponding. to and 87 respectively, of the length of the blade, and disclose a cambered thrust face 8, having a cambe; or convex curvature which is preferably greater than one-third the camber or convex curvature on the conventional back or suction face. Between approximately (E and 75% of the blade length, a transitional zone on the thrust face exists, and in this zone the thrust face is gradually cambered or convexly'curved.

By the present invention, there is provided a propeller blade which is not only unusually efiicient in operation but which may be easily and readily constructed. By forming the outer end portion of the blade in such a manner that both faces thereof are convexly curved, a substantial increase in the efficiency of the blade is secured, especially when air velocities of 900 feet per second or more are encountered by this portion of the blade.

While one form only of the invention has been illustrated'and described, it is to be ex pressly understood that the same is not limited thereto but may be embodied in other forms. For example, though it has been stated that the camber on the thrust face of the blade adjacent the outer end portion thereof is preferably greater than one-third the camber on the suction. face of the blade, it is to be understood that the camber of the thrust face may be less than the camber or the convex curvatureof the suction face if desired. Other changes may also be made in the construction of the blade as well understood by those skilled in the art without departing from the spirit of the invention. Reference will therefore be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. A propeller blade composed of symmetrical convex aerofoil sections adjacent the outer extremity thereof and having aerofoil sections including a relatively flat face at approximately the central portion thereof.

2. A propeller blade composed of aerofoil sections of the double convex type adjacent the outer end portion of said blade and having aerofoil sections of the type with a relatively fiat face and an .opposed convex face adjacent the central portion of said blade.

3. A propeller blade-having a thrust face and a camber face, said thrust face being relatively flat for the greater length of said blade and relatively convexed for the length of the blade adjacent the outer end portion thereof.

4. A propeller blade composed of aerofoil sections, said sections in the central portion of said blade having a relatively flat thrust face and in the outer extremity of said blade having a relatively convexed thrust face, a transition zone interposed between the relatively flat and the relatively convex thrust faces, said thrust face gradually convexed in said zone toward the outer extremity of said blade.

5. A propeller blade having a thrust face, said face having a relatively flat surface for the greater length of the blade and a convex surface for the length adjacent the outer extremity of said blade.

6. A propeller blade having a thrust face and a suction face, said thrust face having a relatively flat surface for the greater length of said blade and a cambered-surface' for the lengthadjacent the outer end of said 'blade said cambered surface. having a curvature of more than one-third the curvature of the camber on the suction face adjacent the outer end of said blade.

7. A propeller blade having a thrust face, said face having a relatively fiat surface from a point approximately one-third of the length of the blade to a point approximately twothirds of the length of said blade and having also a cambered surface from a point approx- -imately three-quarters of the length of said blade to the tip of said blade, there being a transition zone between said flat and cambercd surfaces of the thrust face, said thrust face gradually cambered in said zone.

8. A- propeller blade having two opposite faces, one face cambered for the entire ength of said blade, the other face having a relatively flat surface for a substantial portion of the length of said blade and having a cambered surface for the portion adjacent the extremity of said blade.

9. A propeller blade having two opposite faces, one face cambered' for the entire length of said blade, the other face having a relatively flatsurface for a substantial portion of the length of said blade and having a cambered surface for that portion of its length where the air velocity traversing said surface will exceed, in normal operation, 900 feet per second.

In testimony whereof, I have hereunto signed my name.

MARSHALL A. SMITH, JR. 

